1. Field of the Invention
The present invention relates to a photoelectric conversion device, and system and an image reading method using the photoelectric conversion device. More specifically, the invention relates to a photoelectric conversion device that is suitably used in radiation equipment such as an X-ray apparatus, a system and an image reading method using the photoelectric conversion device.
2. Description of the Related Art
In X-ray photographing for medical diagnosis purposes or for non-destructive testing of the internal structure of a test sample without destroying the sample, an X-ray photography uses an intensifying screen and an X-ray photographic film in combination in a still photograph fashion. In such photographing, when radioactive rays such as X-rays, that are transmitted through a specimen such as a human body or other objects, are incident on an intensifying screen, fluorescent materials contained in the intensifying screen absorb X-ray energy and emit fluorescence.
The X-ray photographic film is exposed to the fluorescence, and an X-ray image is formed on the film. The film is subjected to development and fixing processes to make the X-ray image visible.
A variety of techniques for digitally reading such an X-ray image have been recently developed. For example, one technique employs X-ray imaging means including an X-ray sensitive photoelectric conversion device which converts detected X-rays into an electrical signal according to the intensity of the X-rays, a fluorescent body capable of absorbing X-ray energy that emits fluorescence in accordance with the intensity of the X-rays, and a visible light sensitive photoelectric conversion device which converts the visible light into an electrical signal according to the intensity of the visible light. According to this technique, an X-ray image is converted into an electrical signal, which is then A/D converted and read digitally.
European Unexamined Patent Publication EP0660421A discloses one example of a photoelectric conversion element that uses amorphous silicon (a-Si) as a photoelectric conversion material.
FIG. 1 is a schematic diagram of a photoelectric conversion device incorporating this photoelectric conversion element. As shown, S11 through S44 are photoelectric conversion elements. T11 through T44 are switching TFTs (thin film transistors). A reading power supply Vs and a refresh power supply Vr are connected to the drains of photoelectric conversion elements S11 through S44 via switches SWs and SWr, respectively. The SWs is connected via an inverter to a refresh control circuit RF and the switch SWr is directly connected to the refresh control circuit RF. The switch SWr is on during the refresh period and the switch SWs is on for the rest of time. Also shown are refresh lines rf, gate driving lines g1 through g4, reading lines o1 through o3, and shift registers SR1 and SR2.
One pixel or cell is constructed of a photoelectric conversion element and a switching TFT, and the output signal of the cells selected by the shift register SR1 as a row address selection circuit is sequentially output by the shift register SR 2 as a transfer circuit and is then amplified by an Amp to a desired level.